Previous studies have found that nicotine/mecamylamine treatment more than doubles the long-term abstinence rates relative to nicotine replacement alone. Recent evidence supports the hypothesis that nicotine/mecamylamine treatment prior to smoking cessation partially blocks the rewarding effects of cigarette smoking and hence promotes extinction of the smoking habit, facilitating subsequent abstinence. The behavioral approach employed is also an extinction strategy and involves having smokers switch to de-nicotinized tobacco cigarettes for two weeks prior to quitting smoking. It is hypothesized that the use of de-nicotinized cigarettes might provide more complete extinction than provided by the partial pharmacologic blockade using nicotine/mecamylamine alone. The pharmacologic treatment was expected to increase compliance with the de-nicotinized cigarette smoking regimen, because subjects' usual brands of cigarettes will be less appealing than in the absence of nicotine/mecamylamine treatment. Together the brand-switching and nicotine/mecamylamine therapies were expected to reduce cravings and other withdrawal symptoms as well as increase long-term abstinence from smoking.